1. Field of the Invention
The present invention relates to an apparatus for integrating an electrolytic corrosion associated voltage. More specifically, the present invention relates to an apparatus for providing an indication qualitatively associated with an amount of electrolytic corrosion which occurs in an electric conductor installed in contact with the earth.
2. Description of the Prior Art
In almost all electric railways, the electric cars are energized by a DC voltage source. Typically, a DC voltage is supplied between a supply line and a rail in view of the fact that the rail is a good electric conductor. The electric car is thus supplied with the electric power from a supply line and a rail, while the car moves along the rail. The fact that the rail is installed in contact with the earth, however, can cause an undesirable situation. More specifically, as is often the case with a city or town, other electric conductors, such as water pipes, gas pipes, telephone cables, power cables and the like, are installed in the earth, which can extend along and in the vicinity of the rails of the electric railways. Therefore, it can often occur that a portion of the power current of the electric railways flows through the earth and the adjacent other electric conductors by way of leakage. It has been well known that electric conductors, such as rails, pipes, cables or the like, installed in contact with the earth are corroded in an electrolytic manner, as a result of leakage current or corrosion current flowing from the conductor to the earth. Thus, it is most important that those who maintain such electric conductors are aware of tendency of such corrosion occurring in the conductor.
A typical prior art method of providing an indication qualitatively associated with an amount of the corrosion occurring in an electric conductor installed in contact with the earth is as follows. A change in voltage as measured between an electric conductor and an earthed reference electrode installed in ideal, good electric contact with the earth is recorded on a record medium, such as a record sheet. The area of the waveform thus obtained is calculated. It is well known that the above-mentioned conductor-to-earthed reference electrode potential is qualitatively associated with the above-mentioned leakage current and the area of the waveform thus obtained is qualitatively associated with the quantity of electricity carried by the leakage current, which is closely related to the amount of the corrosion. However, such a method is disadvantageous in that it is very tiresome and of low accuracy. Another prior art approach to provide an indication associated with the amount of corrosion comprises utilization of a silver or copper coulometer, in which the amount, and specifically the weight, of silver or copper deposited within the coulometer due to the flow of leakage current caused by the conductor-to-earthed reference electrode potential indicates the leakage current, and thus the amount of corrosion. This approach is also of low accuracy. It is desired to provide an apparatus capable of providing with accuracy and ease an indication of the above-mentioned area of the waveform of the conductor-to-earthed reference electrode potential, which is qualitatively associated with the amount of electrolytic corrosion which occurs in an electric conductor installed in contact with the earth.
A voltage storing device of interest in connection with the present invention is disclosed in U.S. Pat. No. 3,753,110, issued Aug. 14, 1973 to Hironosuke Ikeda et al and assigned to Sanyo Electric Co., Ltd., the same assignee as that of the present invention. As set forth in the referenced patent, Professor Takehiko Takahashi and Assistant Professor Osamu Yamamoto, Technological Department of Nagoya University, announced their study on the electrochemical potential memory device by the use of a solid state electrolyte at the 22nd annual assembly of Japan Chemical Association held on Apr. 5th to 7th, 1979. Briefly stated, this device comprises an Ag electrode as a cathode, an Ag-Te alloy electrode as an anode, and a solid state electrolyte having high ion conductivity, such as RbAg.sub.4 I.sub.5 sandwiched between both electrodes. When a DC voltage is applied to the device so that the Ag electrode may be negative, a portion of Ag contained in the Ag-Te alloy electrode migrates over to the Ag electrode, resulting in a decreased activity of Ag in the Ag-Te alloy, and thus an increased potential difference between both electrodes. The inventors of this device termed this state of operation as "charging." When the polarity of the applied DC voltage is reversed to that of the former case, Ag migrates back to, and is refilled into, the Ag-Te alloy, resulting in the potential difference decreasing and returning to the initial value eventually. The inventors of this device termed this state of operation as "discharging." Study disclosed by the inventors of this device indicated that the electromotive force generated by the above-mentioned charging or discharging current underwent linear change to some extent with respect to the charging or discharging quantity of electricity (current.multidot.time). Thus, this device makes it possible, as an outstanding characteristic, to do write-in and non-destructive read-out operations while preserving a relatively linear relation between the charging or discharging time and terminal voltage, and in addition, it can hold the memory condition for a relatively long period of time. These advantages mean that this device has potential use as an analog memory device. The referenced patent further discloses an improved electrochemical potential memory device. More specifically, FIG. 6 of the referenced patent shows both an improved electrochemical potential memory device for eliminating the IR drop across the resistance of the electrolyte and the overvoltage caused by dissolution or deposition of Ag, which improved device is basically characterized by the provision of an auxiliary cathode that comprises an output terminal for detecting the potential separately from the above-mentioned cathode utilized as the input terminal for the current conduction.
In view of these advantageous characteristics of the above-mentioned memory device, it may be possible to utilize this device as an essential component of an apparatus for obtaining information relative to electrolytic corrosion by measuring the quantity of electricity flowing therethrough as a result of the application thereto of the above-mentioned conductor-to-earthed reference electrode potential which is qualitatively associated with the leakage current flowing from or to an electric conductor installed in contact with the earth. A prior art apparatus of interest for integrating an electrolytic corrosion associated voltage for realizing the above-mentioned possibility has been disclosed in U.S. patent application, Ser. No. 575,998, entitled "APPARATUS FOR MEASURING ELECTROLYTIC CORROSION," now U.S. Pat. No. 4,003,815, and assigned to Sanyo Electric Co., Ltd., the same assignee as the present invention. More specifically, the referenced application discloses an apparatus for integrating an electrolytic corrosion associated voltage, comprising a solid state electrochemical potential memory device connected to an electric conductor installed in electrical contact with the earth, and to an earthed reference electrode, and means for reading out the output voltage of the said potential memory device. The solid state electrochemical potential memory device exhibits a terminal voltage between an anode and a cathode, which voltage is linearly changing as a function of the charging or discharging quantity of electricity fed to the device, the memory device being capable of holding the terminal voltage. The potential memory device is charged or discharged as a function of the current caused by the conductor-to-earthed reference electrode potential to flow through the said potential memory device from or to the said electric conductor, which current is qualitatively associated with corrosion current flowing through the said electric conductor. Therefore, an output of the memory device as charged or discharged in a predetermined period of time is qualitatively associated with the amount of electrolytic corrosion which is caused by the said leakage current. As a result, tendency of such corrosion can be known.
Nevertheless, the measurement with the electrolytic corrosion associated voltage integrating apparatus disclosed in the cited application is of low accuracy in certain applications such as measurement of the corrosion in an electric conductor, the conductor-to-earthed reference electrode potential of which is low. More specifically, even though an earthed reference electrode is installed to be in ideal, good electrical contact with the earth, the installation of such an earthed reference electrode inherently entails the experiencing of a potential difference between the electrode and the earth per se, which potential difference is characteristic of the material of the reference electrode. Therefore, in the case where a corrosion current is rather small and a conductor-to-earthed reference electrode potential is accordingly low in a certain environment of corrosion measurement, the above-mentioned potential difference proper to the reference electrode material becomes dominant as compared with the conductor-to-earthed reference electrode potential of interest, resulting in low accuracy. It is desired to provide an apparatus capable of providing an integrated indication of conductor-to-earthed reference electrode potential with high accuracy and ease in any environment of such corrosion measurement.